The Theory of Constraints

In the industry, a widely used method is the Theory of Constraints, sometimes without being named. This theory helps focus efforts in the right place, to achieve the maximum results. In this article, I’ll start by explaining the TOC (Theory of Constraints), then I will give you tips to use it on a daily basis.

Principle of the Theory Of Constraints

Since the strength of the chain is determined by the weakest link, then the first step to improve an organization must be to identify the weakest link.

Eliyahu M. Goldratt (1947 – 2011), Israeli business management guru
Author of The Goal: a Process of Ongoing Improvement

In his book, Goldratt gives several examples to illustrate the Theory Of Constraints. Besides the steel chain, and its weakest link, the troop of Scouts in the forest marked me very much.

Indeed, even if some young people are faster, the Scout troop will only arrive at the camp when all the Scouts have arrived. Even if they are not physically connected, it is the slowest that dictates the rhythm.

The performance of the troop depends on the proper use of resources. If the slowest one carries the heaviest bag, he will be even slower. If he has to go to the fastest pace, he will go “overheat”. A stitch or shortness of breath would slow down the group even more.

By having everyone to stand on his slower pace, we preserve the resources. It is then possible to carry his bag for example, to speed up his pace and that of the team.

The rhythm of the production line, its takt time, is conditioned by that of the slowest equipment.

How to identify the bottleneck

Commonly referred to as a bottleneck, the constraint equipment is generally easy to identify. During a Gemba, you will quickly see or locate accumulated stocks. Take the time to observe the situation, because it is not always so obvious. Remember the story of the Hare and the Tortoise. Faster equipment can encourage its operators to take breaks or go help elsewhere. The stock then accumulates at the entrance of the equipment, which is not bottleneck.

You can use a mapping such as VSM (Value Stream Mapping), with the working time on each equipment to help you. You can also question operators, who are often very aware of the production bottlenecks. Routings can also guide you. In the end, what is important is that you are sure to address the equipment that generates the constraints. The weak links in your factory somehow.

How to remove the bottleneck

Then it is the time of observation. You need to determine why this equipment is causing a bottleneck. It is necessary to make a precise diagnosis in order to address root causes. Using several times the 5 Why, you will draw a causes tree. Then you can decide on the right plan of action.

Here are some examples of common causes:

  • The equipment is not reliable. The operator has to make adjustments frequently. He checks the parts a lot. He adjusts the equipment during production. Or he even rework some parts twice to succeed. In this situation, it is the Six Sigma methodology that will help you reduce the variability in production.
  • The equipment is long to prepare for each new series. You work with smaller series, but this equipment takes time to settle. You have increased the batch sizes, but it does not meet the need. In this case, it is the SMED that will help reduce the time required to switch from one type of product to another.
  • The workstation is overall disorganized. The operator does a lot of manipulation. He moves the pieces several times, makes many round-trips. In this case, you’ll have to start with a spaghetti diagram. You can then improve the flow and especially the ergonomics of the workstation. You may be reorganizing the teams or prioritization.

Finalize the SMED construction site

In any case, you will not forget to use the 5S to finalize your improvement workshop. It is usually with a Kaikaku approach that the bottleneck is corrected. A team works for a few days to solve the constraint.

To remember

Theory of Constraints improves the performance of the entire value chain. Here are 5 steps to remember to apply it.

  1. Identify the system’s bottlenecks.
  2. Decide how to exploit the bottlenecks.
  3. Subordinate everything else to the above decision.
  4. Elevate the system’s bottlenecks.
  5. If, in a previous step, a bottleneck has been broken go back to step 1.

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